A system including an electrically powered device that generates rotational driving force, a transmission device that changes the speed of the rotational driving force generated by the electrically powered device and transmits that force to a driving target, and the driving target that is driven by the rotational driving force from the electrically powered device can be given as an example of a variable electric motor system.
Patent Document 1 listed below discloses this type of variable electric motor system. The transmission device of this variable electric motor system is a planet gear transmission device. The transmission device includes a sun gear that rotates about the axis, a plurality of planet gears that mesh with the sun gear and revolve around the axis as well as rotating about their own center lines, an arm or carrier that supports the plurality of planet gears, and an internal gear that has a plurality of teeth arranged in an annular shape around the axis and that meshes with the planet gears. An arm shaft extending in the axial direction centered on the axis is fixed to the arm. This arm shaft constitutes an output shaft connected to the driving target.
The electrically powered device of this variable electric motor system includes a sub-motor that rotates the sun gear about the axis, a transmission mechanism that transmits rotational driving force of the sub-motor to the sun gear, a main motor that rotates the internal gear about the axis, and a transmission mechanism that transmits rotational driving force of the main motor to the internal gear. A rotor shaft of the sub-motor and a rotor shaft of the main motor are both disposed parallel to the axis of the transmission device and distanced from that axis in a radial direction. Each transmission mechanism includes belts and pulleys.
According to this variable electric motor system, the RPM of the output shaft connected to the driving target can be changed by changing the RPM of the sub-motor.